Synthesized frequency sweeps based on fractional-N phase locked loops (PLL) can achieve accurate frequency sweeps. This method of signal generation is preferred in certain applications due to some of its desirable attributes such as accuracy, frequency range, spur level, and power consumption. When a traditional fractional-N divider is used, the output frequency is either proportional to time or reciprocal of time, respectively, depending on whether the fractional-N divider is used in the feedback path or as the reference divider. With the new fractional-N divider of this invention, the fractional divide ratio is a function of polynomials to allow changing the frequency profile through its coefficients.
When this new fractional-N divider is used in the feedback path of a PLL, the output frequency profile changes from a linear function of time to that of a polynomial function of time, allowing non-linear frequency profiles to be produced. When this new fractional-N divider is used as the reference divider of a PLL, its polynomial coefficients can be used to linearize the output frequency profile.
The traditional methods of non-linear synthesized sweeps are linear piece-wise approximation and point-to-point steeping from a frequency list.
In the case of sweep linearization, the traditional method is piece-wise approximation with small enough spans to minimize linearization error.
Certain applications tolerate sweep non-linearity using post-processing correction, which is a data processing method rather than a signal generation method.